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Tantalum is widely used in chemical engineering due to its outstanding corrosion resistance in a wide range of conditions. Tantalum is generally more corrosion resistant than titanium, zirconium or niobium.

More information about Tantalum

Tantalum is a chemical element with the symbol Ta and atomic number 73. A rare, hard, blue-gray, lustrous transition metal, tantalum is highly corrosion resistant and occurs naturally in the mineral tantalite, always together with the chemically similar niobium. It is part of the refractory metals group, which are widely used as minor component in alloys. The chemical inertness of tantalum makes it a valuable substance for laboratory equipment and a substitute for platinum, but its main use today is in tantalum capacitors in electronic equipment.

Characteristics

Physical

Tantalum is dark, dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to corrosion by acids; in fact, at temperatures below 150 °C tantalum is almost completely immune to attack by the normally aggressive aqua regia. It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulfur trioxide, as well as with a solution of potassium hydroxide. Tantalum's high melting point of 3017 °C (boiling point 5458 °C) is exceeded only by tungsten and rhenium for metals, and carbon.

Chemical

It is able to form oxides with the oxidation states +5 (Ta2O5) and +4 (TaO2),[17] The most stable oxidation state is +5, tantalum pentoxide.[17] Tantalum pentoxide is the starting material for several tantalum compounds. The compounds are created by dissolving the pentoxide in basic hydroxide solutions or by melting it in another metal oxide. Such examples are lithium tantalate (LiTaO3) and lanthanum tantalate (LaTaO4). In the lithium tantalate, the tantalate ion TaO−3 does not occur; instead, this part of the formula represents linkage of TaO7−6 octahedra to form a three-dimensionalperovskite framework; while the lanthanum tantalate contains lone TaO3−4 tetrahedral groups.[17]

The fluorides of tantalum can be used for its separation from niobium.[18] Tantalum forms halogen compounds in the oxidation states of +5, +4, and +3 of the type TaX5, TaX4, and TaX3, although multi core complexes and substoichiometric compounds are also known.[17][19] Tantalum pentafluoride (TaF5) is a white solid with a melting point of 97.0 °C and tantalum pentachloride (TaCl5) is a white solid with a melting point of 247.4 °C. Tantalum pentachloride is hydrolyzed by water and reacts with additional tantalum at elevated temperatures by forming the black and highly hygroscopic tantalum tetrachloride (TaCl4). While the trihalogen compounds can be obtained by reduction of the pentahalogenes with hydrogen, the dihalogen compounds do not exist.[17] A tantalum-tellurium alloy forms quasicrystals.[17] Tantalum compounds with oxidation states as low as -1 have been reported in 2008.[20]

Like most of the other refractory metals, the hardest known compounds are the stable nitrides and carbides. Tantalum carbide, TaC, like the more commonly used tungsten carbide, is a very hard ceramic that is used in cutting tools. Tantalum (III) nitride is used as a thin film insulator in some microelectronic fabrication processes.[21] Chemists at the Los Alamos National Laboratory in the United States have developed a tantalum carbide-graphite composite material that is one of the hardest materials ever synthesized. Korean researchers have developed an amorphous tantalum-tungsten-copper alloy that is more flexible and two to three times stronger than commonly-used steel alloys.[22] There are two tantalum aluminides, TaAl3 and Ta3Al. These are stable, refractory, and reflective, and they have been proposed[23] as coatings for use in infrared wave mirrors.

Applications

Electronics

The major use for tantalum, as the metal powder, is in the production of electronic components, mainly capacitors and some high-power resistors[35]. Tantalum electrolytic capacitors exploit the tendency of tantalum to form a protective oxide surface layer, using tantalum powder, pressed into a pellet shape, as one "plate" of the capacitor, the oxide as the dielectric, and an electrolytic solution or conductive solid as the other "plate". Because the dielectric layer can be very thin (thinner than the similar layer in, for instance, an aluminium electrolytic capacitor), a high capacitance can be achieved in a small volume. Because of the size and weight advantages, tantalum capacitors are attractive for portable telephones, personal computers, and automotive electronics.[36]

Alloys

Tantalum is also used to produce a variety of alloys that have high melting points, are strong and have good ductility. Alloyed with other metals, it is also used in making carbide tools for metalworking equipment and in the production of superalloys for jet engine components, chemical process equipment, nuclear reactors, and missile parts.[36][37] Because of its ductility, tantalum can be drawn into fine wires or filaments, which are used for evaporating metals such as aluminium. Due to the fact that it resists attack by body fluids and is nonirritating, tantalum is widely used in making surgical instruments and implants. For example, porous tantalum coatings are used in the construction of orthopedic implants due to tantalum's ability to form a direct bond to hard tissue.[38]

Tantalum is inert against most acids except hydrofluoric acid and hot sulfuric acid, also hot alkaline solutions cause tantalum to corrode. This property makes it an ideal metal for chemical reaction vessels and pipes for corrosive liquids. Heat exchanging coils for the steam heating of hydrochloric acid are made from tantalum.[39] Tantalum was extensively used in the production of ultra high frequency electron tubes for radio transmitters. The tantalum is capable of capturing oxygen and nitrogen by forming nitrides and oxides and therefore helps to sustain the high vacuum needed for the tubes.[18][39]

Other uses

The oxide is used to make special high refractive index glass for camera lenses.[40] The high melting point and oxidation resistance lead to the use of the metal in the production of vacuum furnace parts. Due to its high density, shaped charge and explosively formed penetrator liners have been constructed from tantalum.[41] Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point.[42][43] It is also occasionally used in precious watches e.g. from Hublot, Montblanc and Panerai. Tantalum is also highly bio inert and is used as an orthopedic implant material.[44]